Cleaning processes typically play an important role in the formation integrated circuit (i.e., semiconductor) devices. Specifically, the cleaning processes are often necessary since wafers utilized in the devices usually become contaminated during processing.
The need for contaminant removal may be heightened since the devices tend to be more highly integrated, thus containing finer surface patterns. Conventional cleaning methods typically include dry and wet cleaning methods. In one example, a silicon wafer may be immersed in a cleaning bath containing a solution in order to remove various contaminants which may be present on the surface of the wafer. Examples of conventional solutions include RCA Standard Cleaning-1("SC-1") which is an aqueous mixture of ammonia, hydrogen peroxide, and deionized water; RCA Standard Cleaning-2 ("SC-2") which an aqueous mixture of hydrochloric acid, hydrogen peroxide, and deionized water; "SPM" which is an aqueous mixture of sulfuric acid and hydrogen peroxide; and "DHF" which is an aqueous mixture of hydrofluoric acid and deionized water. The SC-1 and SPM cleaning solutions have been often shown to remove various organic materials and contaminated particles present on a wafer surface. The SC-2 cleaning solution is capable of removing metal contaminants. Nonetheless, potential problems exist with respect to using the above solutions. More particularly, chemical oxide films may be formed due to the presence of aqueous hydrogen peroxide. In an attempt to remove the chemical oxide films, the DHF cleaning solution is typically employed.
The use of such a wet cleaning solution, however, may present problems. For instance, as the diameter of silicon wafers increase, the quantity of cleaning solution and deionized water needed to clean the wafer tends to also increase. As a result, heightened environmental risks may occur along with increased costs. Furthermore, a natural oxide film often results on the wafer surface, due to the wafer surface coming in contact with air while performing a cleaning process or prior to performing a subsequent process. Moreover, it is often difficult to incorporate a wet cleaning apparatus into an integrated circuit device fabrication system.
In an attempt to confront potential problems associated with wet cleaning solutions, dry cleaning methods have been proposed. One example of a dry cleaning method using anhydrous hydrogen fluoride and water vapor has been proposed. An improvement thereof is a gas-phase cleaning method using anhydrous hydrogen fluoride and alcohol vapor.
Dry cleaning methods may be more advantageous than wet cleaning methods in that they may present less potential environmental hazards. Moreover, a dry cleaning apparatus may be more easily incorporated into an integrated circuit device fabrication system. A silicon wafer surface exposed to a dry cleaning process also tends to be less susceptible to a natural oxide film formation since it is scarcely exposed to the air to be left as it is during the process. The dry cleaning process may also be effective at removing chemical oxide films that potentially form on the wafer surface. In spite of any perceived advantages, a dry cleaning method using anhydrous hydrogen fluoride and water vapor or alcohol vapor may be potentially ineffective at removing metal contaminants from a wafer surface.
Another example of a dry cleaning method has been proposed in U.S. Pat. No. 4,749,440. Specifically, the '440 patent proposes a method for removing an oxide film from a silicon wafer surface using anhydrous hydrogen fluoride gas. The proposed method, however, suffers from a potential shortcoming in that the wafer may eventually become disuniformly etched. Moreover, various contaminants (e.g., particles and metals) often are not sufficiently removed from the wafer surface.
In light of the above, research efforts have focused on improved methods for removing both metal and particle contaminants from the wafer surfaces. An example of one attempt involves a method which uses ultraviolet light in conjunction with chlorine gas. Specifically, chlorine gas is introduced on the substrate surface to potentially treat the metals and particles. Ultraviolet rays are thereafter irradiated onto the substrate surface. The method, however, is typically only effective at removing aluminum and zinc metals since these metals are able to react with chlorine under the low vapor pressure conditions which are employed.
In addition to the above, U.S. Pat. No. 5,169,408 proposes a cleaning apparatus for in-situ rinsing a semiconductor wafer using deionized rinse water.
There remains a need in the art to provide apparatuses and methods for cleaning wafers used in integrated circuit devices, which potentially are able to remove a wide variety of contaminants. There is also a need in the art to provide apparatuses and methods for cleaning wafers used in integrated circuit devices, which prevent the possibility of natural oxide film formation on the surfaces of the wafers.